Chemical process



Patented Aug. 11, 1953 warren STATES PATENT FFEE No Drawing. Application March 24, 1951, Serial No. 217,403

4 Claims.

This invention relates to a process for the improvement of water-soluble, nitrogen-phosphorus-containing compounds. Such compounds are of utility in fiameproofing compositions.

It has been found that the reaction product of phosphorus oxychloride and ammonia as prepared at temperatures below 100 followed by heat treatment at temperatures in the range of 110150 is obtained as a water-soluble, phosphorus-nitrogen-containing product which, after the removal of ammonium chloride, is substantially neutral or slightly alkaline so that such materials may be applied to fabrics without deterioration of fibers forming the fabric. These chemical compositions are described in copending application Serial No. 169,513, filed June 21, 1950, assigned to the same assignee as is the present application.

It has now been discovered that such phosphorus-nitrogen condensation products may be improved in fiameproofing properties by the treatment thereof with an organic acid. It has been found that any carboxylic acid having from 2 to 4 carbon atoms may be employed for this purpose, a preferred acid being acetic acid. The acids may be employed in anhydrous form, or in solution such as in water. The phosphorus-nitrogen condensation product may be contacted with the acid at any desired concentration, although a preferred range is 25% to 100% of the acid in water and at such temperatures and pressures as may be desired since these are not critical variables. The phosphorus-nitrogen composition is water-soluble, so that it may also be used in aqueous solution in the present process. The proportion of acid relative to the phosphorus-nitrogen compound may be varied widely, although it is preferred to employ at least 25% by weight of the acid relative to the composition to be treated.

The phosphorus-nitrogen condensation product in the form of a white powder may be added to a vat of the acid while stirring the mixture. After such contacting, the acid may be withdrawn by filtration, leaving the modified phosphorus-nitrogen condensation product behind. The damp material may then be dried or may be washed with methanol or acetone to remove water and residual acid. However, solutions of the phosphorus-nitrogen compound may also be employed in the present process. Such solutions using water as a solvent may be contacted with the organic acid to precipitate the acid-insoluble material which exhibits superior properties as set forth in the examples below.

The phosphorus-nitrogen compound may be 2 prepared by the reaction of anhydrous ammonia with phosphorus oxychloride in a solvent. The phosphorus oxychloride so dissolved is then reacted with ammonia ,in gaseous or liquid form with suitable agitation. The temperature should be maintained below C. during the addition of the ammonia. However, after the addition of at least the stoichiometric proportion of ammonia (5 moles per mole of P0013) the temperature is raised and the product heated to at least C. but not above 150 C. It has been found that the temperature control within the above limits is essential to prevent the formation of a Waterinsoluble product on the one hand, and on the other hand to alter the intermediate product so that the subsequent separation and purification steps can be carried out successfully. The reaction of phosphorus oxychloride with anhydrous ammonia, followed by heating the reaction product to at least 110 C1, but not above 150 C., yields the desired composition in aform insoluble in liquid anhydrous ammonia. Ammonium chlo- 7 ride is formed as a Joy-product by reaction of ammonia with the chlorine present in the phosphorus oxychloride. As a result of the conditions under which the present product is prepared, it has been found to be possible to form the nitrogen-phosphorus product so that it possesses solubility characteristics enabling the subsequent separation of the product from the ammonium chloride to be carried out by differential solubility methods. At the same time the desired product is obtained in a form which is highly reactive with cellulose.

In order to show in further detail the method of preparing the phosphorus-nitrogen compound, the following process illustrates the procedure. Phosphorus oxychloride to the amount of 90 pounds is dissolved in 90 gallons of hexane contained in an autoclave. The solution is heated to approximately 55 C. while stirring, and gaseous anhydrous ammonia is added thereto. Although an exothermic reaction takes place, the reaction may be carried out at about 75 C. by cooling the vessel. Ammonia to the extent of 50 pounds (5 moles per mole of phosphorus oxychloride) is added to the autoclave over a two hour period. An excess of ammonia may be used. After the addition of this amount of ammonia, the autoclave is sealed and then heated to about C. for approximately 1 hours. After the completion of the heating period, the reaction mixture is cooled to below 40 C. and then transferred to a second vessel containing a filter element and provided with external heating means.

By applying heat to the autoclave contents the aexane present is distilled oil, condensed and recovered. The remaining solids which consist )f a mixture of the nitrogenand phosphorus- :ontaining product with ammonium chloride are ;hen extracted under pressure with anhydrous ammonia at about room temperature. A total of about 20 pounds of ammonia per ound of final oroduct is employed, although it is also possible 30 carry out an extraction with pounds of ammonia per pound of product. The slurry of oroduct in anhydrous liquid ammonia was filtered 2y means of a filtering device contained within :he autoclave. In this manner, substantially all of the ammonium chloride is leached from. the residual solids. After the last extraction the residual ammonia adhering to the product is rernoved by evaporation induced by the application of heat to the product. The yield of the nitro enhosphorus product obtained is approximately 85% of the theoretical. The product :ontains 33.8% nitrogen, 35.1% phosphorus, N/P ratio=2.14.

The temperature at which the init al reaction )f ammonia and phosphorus oxvchloride is carried out should be maintained below 100 C. Apaarently there is no lower limit to this tempera- ;ure since the reaction has been successfully carried out at extremely low tem eratures. However. the subseouent heating of the first-formed reaction product should be carried out at a temoerature of at least 110 0., but not in excess of 150 0. Moreover, the temperatures within this range are somewhat dependent upon the time of heating the product: at the higher temperatures the time is shorter, while at lower temperatures the time is correspondingly longer. Thus when employin temperatures as high as 150 0.. the time of heating should not be substantially in excess of 30 minutes. When employin temperatures as low as 110 0., the time of heating should be at least six hours, since the initial nitrogenphosphorus-containing product is soluble in liouid anhydrous ammonia while the product which has been heated within the above range of temberatures is insoluble in this same solvent. The :orrect time of heating at any temperature may be readily determined by observation of the soluoility property.

The nature of the nitrogen-phosphorus-containing product has not been completely determined, but it would appear that the product consists of a mixture of closely related compounds probably containing the group:

However, the compounds present in the mixture contain additional radicals, since the phosohorus-nitrogen ratio of our products is greater than 2.0, being in the range of from 2.1 to 2.3, depending upon the temperature employed in the heating step. The molecular weight of the nitrogen-phosphorus product as determined cryoscoplcally is in the range of from 180 to 300, a preferred range being from 200 to 250.

The product so obtained is soluble in water, the 9H thereof being in the range of from 7.0 to 8.5.

The following examples illustrate certain emoodiments of the present invention:

EXAMPLE 1 To a solution containing 80 ml. of water and 20 z. of the water-soluble phosphorus-nitrogen-containing condensation product prepared in accordance with the above method, there was added ml. of glacial acetic acid. The solution was stirred to mix the components and was then allowed to stand for one hour. It was found that the phosphorus-nitrogen condensation product was partially insoluble in the acetic acid solution so that the insoluble material could be filtered off leaving the acid-soluble components in solution. The filter cake obtained from the filtration 'step was then washed with dilute acetic acid and was then further washed with methanol to remove all of the acid and aid in drying the material.

The product obtained was modified from the starting material inasmuch as the pH showed a more acidic product, after all of the acid reagent had been removed. The pH of the final product was found to lie in the range of 4 to 6 as contrasted to the alkaline material previous to the treatment with the organic acid.

EXAMPLE 2 The product obtained in Example 1 was dissolved in water to give a 20% solution. This solution was applied to cotton cloth by padding to obtain an 80% pick-up to give a 16% dry addon. The treated cottonwas then dried and cured at 140-150 C. for 10 minutes. The treated material was wash-fast and was found to be flameresistant even after repeated washings. The flame-resistance test was carried out in accordance with the method described by R. W. Little in Flameproofing Textile Material, pages 111- 115 (Reinhold Publishing 00., 19a?) rial was also found to resist tendering better than conventional flame-resisting treatments.

EXAMPLE 3 A sample of sheeting-weight cotton cloth was treated as described in Example 2 with a similar solution of the acid-insoluble phosphorus-nitrogen condensation product of Example 1. By employing a similar wet pick-up it was found that an add-on of about 17% (dry basis) was readily obtained. The wet material was dried and was then cured at C. for ten minutes. The treated material withstood the conventional flame-resistance treatment as described above. The treated material was also tested to determine its tear strength. It was found that the tear strength as carried out under standard conditions was 1360 grams. A control sample not subjected to the present treatment when tested under the same conditions gave a warp strength of 1232 grams. showing that the treated material in addition to being flame-resistant also exhibited an increase in strength over the original material.

EXAMPLE 4 1 A sample of sheeting-weight cotton cloth was impregnated with the acid-extracted phosphorus-nitrogen condensation product as described above and was then cured at a temperature of C. for five minutes as having been previously dried. It was found that this material withstood the standard test for flame-resistance and also showed an increase in strength over the original material. The warp tear strength was 1376 grams as contrasted to a control sample (Control A) which had a warp strength of 1232 grams Without the treatment of the present exam le.

The mate- EXAMPLE 5 In order to show the improvement'in the nitrogen-phosphorus condensation product-as a result of the acid extraction, a test was conducted in which another sample of sheeting-weight cotton was impregnated with the unextractedphosphorue-nitrogen condensation product. Such condensation product, without having been treated with acid, was utilized as 21.20% aqueous solution and was impregnated to the extent of 16% to 18% add-on (dry basis). The treated material was then dried and cured at 140 C. for ten minutes. The fabric was then tested and was found to pass the test for flame-resistance but was found to have a lower tear strength. The warpstrength of a sample was found to be 1168 grams in contrast to a control strip (Control B) not subjected to any chemical treatment and having a warp strength of 1296 grams.

The above test data aresummarized in the table below. It is seen that there is an improvement in theproperties of the cottonwhen the phosphorus-nitrogen compound has been acid-treated since the treated cotton fabric shows less of a tendering efiect and in certain of the examples exhibits an increase in strength as compared to the original untreated material.

In order to show the variation which may be effected in the acid concentration of the present process a series of tests was conducted in which acetic acid-water solutions were prepared in the range of from 25% to 100% acetic acid. These solutions were mixed with portions of the watersoluble, nitrogen-phosphorus condensation product described above. The solutions were agitated and were then filtered to remove the acid-soluble portion from the insoluble product. It was found that the recovery was good in each case and a product obtained which was effective in the treatment of cellulosic materials to impart the property of fire-resistance.

The product obtained with the various acid treatments was useful in the fiameproofing of cellulosic material such as cotton. The data representative of typical examples of acid concen- EXAMPLE 7 A treatment was carried out similarly to Example 1 employing propionic acid in 100% concentration and also in 50% concentration with water. The phosphorus-nitrogen condensation product described above was contacted with the propionic acid solutions and was found to yield a product having improved properties in the treatment of cellulosic materials such .as cotton in order to render the samefire-resistant.

EXAMPLE 8 EXAMPLE 9 "Monochloracetic acid was employed similarly to chloracetic acid as described in Example 1. It was foundthat a 50% solution of monochloracetic acid in water could readily be employed with the phosphorus-nitrogen condensation product either in solid form or in aqueous solution to give a superior product after removal of the acid.

EXAMPLE l0 Trichloracetic acid was employed similarly to acetic acid as described in Example 1. It was found that this acid could likewise be employed in form or as an aqueous solution for the modification of the phosphorus-nitrogencondensation product to yield a composition useful in the flame-retardant treatment of cotton.

EXAMPLE 1 1 The use of oxalic acid in the modification 0f the phosphorus-nitrogen condensation product was shown by the addition of such condensation product as a white powder to a solution of one part of oxalic acid in an equal weight of water. It was found that a pasty composition resulted which could be extracted with methanol to remove the acid and water, leaving the modified phosphorus-nitrogen compound in a form having utility in the treatment of cotton for flame-proofing purposes. It was also found that a 40 solution of the phosphorus-nitrogen compound in water gave a readily filterable product when in contact with oxalic acid. Upon removal of the liquid the modified, residual solid material was found to have excellent properties in flameproofing treatment.

In general, the carboxylic acids having from 2 to 4 carbon atoms have been found to be useful in the process of the present invention. Such acids include acetic, propionic, and butyric acids. In addition to the monocarboxylic acids, it has also been found that substituted acids such as halogen derivatives and dicarboxylic acids also have utility for this purpose. For example, maleic, tartaric, malic, malonic and lactic acids may be employed for the treatment of the nitrogen-phosphorus compound.

What is claimed is:

1. In a process for the improvement of the fireretardant properties of the water-soluble, ammonia-insoluble reaction product of one mole of phosphorus oxychloride and at least five moles of anhydrous ammonia, which reaction product is obtained by the preliminary heating of the said reactants at a temperature below C., followed by heat-treatment thereof at a temperature in the range of 110 C. to C., the improvement which comprises contacting the said reaction product with acetic acid to extract therefrom the acid-soluble components, and thereafter removing such soluble components to obtain the insoluble portion as a material of improved fire-retardant qualities.

2. In a process for the improvement of the fireretardant properties of the water-soluble, ammonia-insoluble reaction product of one mole of phosphorus oxychloride and at least five moles of anhydrous ammonia, which reaction product is obtained by the preliminary heating of the said reactants at a temperature below 110 C., followed by heat-treatment thereof at a temperature in the range of 110 C. to 150 C., the improvement which comprises contacting the said product with propionic acid to extract therefrom the acid-soluble components, and thereafter removing such soluble components to obtain the insoluble portion as a material of improved fireretardant qualities.

3. In a process for the improvement of the fire-retardant properties 01 the water-soluble, ammonia-insoluble reaction product of one mole of phosphorus oxy-chloride and at least five moles of anhydrous ammonia, which reaction product is obtained by the preliminary heating of the said reactants at a, temperature below 110 C., followed by heat-treatment thereof at a temperature in the range of 110 C. to 150 C., the improvement which comprises contacting the said reaction product with butyric acid to extract therefrom the acid-soluble components, and

thereafter removing such soluble components to obtain the insoluble portion as a material of improved fLre-retardant qualities.

4. In a process for the improvement of the fireretardant properties of the water-soluble, ammonia-insoluble reaction product of one mole of phosphorus oxychloride and at least five moles of anhydrous ammonia, which reaction product is obtained by the preliminary heating of the said reactants at a temperature below C., followed by heat-treatment thereof at a temperature in the range of 110 C. to C., the improvement which comprises contacting the said reaction product with a monocarboxylic acid having from 2 to 4 carbon atoms to extract therefrom the acid-soluble components, and thereafter removing such soluble components to obtain the insoluble portion as a material of improved fire-retardant qualities.

MORRIS L. NIELSEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,071,353 Morgan Feb. 23, 1937 2,262,634 Cobbs Nov. 11, 1941 2,286,308 Rosser June 11, 1942 2,305,035 Rosser Dec. 15, 1942 2,415,112 Seymour et a1. Feb. 4, 1947 2,415,113 Seymour et a1. Feb. 4, 1947 2,544,706 Malowan Mar. 13, 1951 

4. IN A PROCESS FOR THE IMPROVEMENT OF THE FIRERETARDANT PROPERTIES OF THE WATER-SOLUBLE, AMMONIA-INSOLUBLE REACTION PRODUCT OF ONE MOLE OF PHOSPHORUS OXYCHLORIDE AND AT LEAST FIVE MOLES OF ANHYDROUS AMMONIA, WHICH REACTION PRODUCT IS OBTAINED BY THE PRELIMINARY HEATING OF THE SAID REACTANTS AT A TEMPERATURE BELOW 110* C., FOLLOWED BY HEAT-TREATMENT THEREOF AT A TEMPERATURE IN THE RANGE OF 110* C. TO 150* C., THE IMPROVEMENT WHICH COMPRISES CONTACTING THE SAID REACTION PRODUCT WITH A MONOCARBOXYLIC ACID HAVING FROM 2 TO 4 CARBON ATOMS TO EXTRACT THEREFROM THE ACID-SOLUBLE COMPONENTS, AND THEREAFTER REMOVING SUCH SOLUBLE COMPONENTS TO OBTAIN THE INSOLUBLE PORTIONS AS A MATERIAL OF IMPROVED FIRE-RETARDANT QUALITIES. 